Gaseous discharge tube



July 4, y1944.

S. G. KLUMB GASEOUS DISCHARGE TUBE Filed April 1o, 1941 @M2M/V Sian/@y 5. .ff/Umb during discharge of the tube, consists of a puddle of mercury. The other positive electrode IIl is formed of a metal which will not amalgamate with mercury and which has sufciently high density to preclude release of trapped gases'.

Ferrous metals have proved satisfactory and Swedish iron has been found exceptionallygood.

In the sense that it is not flowable or fluid like the mercury electrode 9,;the electrode I is solid, and where this term is'used in theclaims it vis to bring out this distinction.

Except for the manner inwhich the puddle of mercury constituting the negative electrode is held within the tube and the shape of the posi. tive electrode I0 and the specific type of ferrous metal of which it is made, both embodimentsv of the invention illustratedare the same..

In both instances the positivev electrode is supported from the dome-shaped top ofthe tube by means of a wire II passing through the ltube wall. The wire II shouldhave substantiallyrthe same coefficient of expansion as lead glass which is used for the tube. Dumet wire meets A this requirement.

In the embodiment of the invention shown in Figure 1 the Dumet wire I I extends down through the tube wall to be connected to and support electrode I0 which in this instanceis a tungsten wire. f

Except for its lower tipwhich forms the electrode proper, this tungsten wireis covered with a suitable insulating sheath I2 In each instance the wire II is fused to a glass bead I3 prior to its assemblywith the tube, and then thebead is fused to the tube.

In the other embodiment of the invention -the electrode I0 is a round rod or piece 'of Swedish iron having its lower end rounded for a'purpose to be hereinafterV described.

In the construction yshown in Figure 1l the pud dle of mercury 9 fills a central well'I'Il formed in a ceramic insert I5. rI'he top'wallof this 'insert slopes upwardly from'the edgeof the well to the periphery of the insert so as toat all times guide the mercury toward and'assure its accumulating` inthewelll4.

The insert I5 substantially fits the bottom 'o'f the tube and is secured inplace by a wire lead I6 having one end fixed to' an' iron washer I'I seated in the bottom Aof the well and 'passing through the tube to have its opposite end soldered to the prong 1. Y

The other'prong 8 has one end of 'a' wire I8 fixed thereto. This wire passes out through a hole in the side of the base and extends upwardly along the exteriorV of vthe tube tov be connected as at I9 to the wire I I and consequently the elec-` trode I0. 1

In the construction shown in Figure 2 the terminal connections for rtheelectrodes are the same as that of Figure 1.','butin-place1ofthe insert I5 a largerquantity of mercury is employed and it pools directly in the bottom ofthe tube as shown.

The rounded lower end of the positive electrode IIl assures the maintenance of the desired spacing between the electrodes even though the tube may be inclined a substantial distance from vertical. As will be apparent the distance between the surface of the mercury and the nearest portion of the electrode I0 remains substantially the same throughout a relatively wide angle of inclination.

With ytheconstruction of AFigure 1 in which the electrode III is substantially'a point, this problem does occur.

This latter construction, however, has the advantage ofkeeping the arc from striking the glass which might cause breakage.

In making the tube, after the various elements are assembled in the manner described, the tube is bakedto. drive off the occludent gases from the walls of the glass, the mercury pool and all internal parts. The tube is then evacuated to as nearly a perfect vacuum as possible and While the tube is physically connected to the vacuum source but, shut off therefrom a desired amount of helium or other suitable inert gas is admitted, Thereafter the tube is sealed in the customary manner which generally leaves a tip 20 and -disconnects it physically from the vacuum source.-

Obviously by controlling the amount of the gas admitted to the tube its internal pressure may be predetermined. The criticalvalue of ,the tube; or, in other words, the voltage required to be impressed across its terminals to cause it-to fire. depends primarily uponl two factors,- onethe spacing between the electrodes, and-twoA the internal pressure of the tube. r

The spacing of the electrodes may vary slightly from the desired amount in different tubes, .but this is of no consequence as will be seen. The important thing with respect to this factorf'is that the spacing will not change'during usage.

The gas pressure, the second factor, is indi-v vidually set for each tubeY yin the following manner: After evacuating. and while the gas ad-` mission takes vplace the tube islconnected in an electric circuit consisting of a condenser across which the tube is connected and aunidirectional pulsating voltage source connected to charge the condenser. A voltmeter connected` 'preferably across the condenser indicates the potential -von' the condenser at which tube discharge; takes place. With a slight amount of inert gas in thev tube, its resistance is low and hence ring of'the tube is frequent and the breakdown potential as measured by the voltmeter is low. With increase in gas pressure -the tube's resistance. rises and so does its critical value. When the voltmeter fin'-` dicates the desired yfiash voltage ,gast admission is stopped and thereafter the tube willVv always re at the value last indicated. 3.6;.- :1T

In View of the .wide temperature range1v thatV tubes of this type are subjected` to 'in use,gt 'he gas used must not be easily affectedby temperature. Helium is known tobestablegin this re-Av spect, but from much experiment itwas learned that unless the helium is spectroscopicallyl p ure the walls of the tube become plated with mercury and the gas pressure varies. With spectroscopie cally pure helium no changes take place-inthe tube constants when the tube is used for such purposes as electric fence controllers where the temperature ranges from A summer heat to extreme winter cold. y Y

As noted hereinbeforethe ions leave the posi-f` tive electrode rIII duringdischarg ofthe tube, but inasmuch as the Itegem@ electrade isifqrmedbi mercury its resultant bombardment in nowise ailiects the constants of the tube.

While it is true that such bombardment causes the mercury to vaporize, this merely results in condensation of the mercury vapor which then drips back into the pool to restore the negative terminal to its initial condition.

By the constants of the tube is meant the space between the electrodes and the pressure of the gas within the tube.

From the foregoing description taken in connection with the accompanyingdrawing it will be readily apparent that this invention provides a gaseous discharge tube capable of withstanding the strenuous service imposed upon such tubes by their use in electric fence controllers, and that the tube is extremely simple and rugged in construction.

What I claim as my invention is:

1. A gaseous discharge tube suitable for controlling the discharge of a condenser in a condenser discharge type electric fence controller wherein the tube must be capable of successfully withstanding relatively heavy loads without change in its factors determining the firing voltage of the tube comprising: an envelope from which air has been evacuated; means for mounting the envelope in an upright position; a pool of mercury in the bottom of the envelope providing a cold cathode; a solid metal electrodeV providing an anode; means supporting the metal electrode in a fixed position in the envelope; the end of the electrode adjacent to the surface of the mercury being of such size and shape that the spacing between it and the mercury remainsA substantially constant throughout a relatively wide range of possible inclination of the envelope from its intended upright position; and an inert gas in said envelope, the pressure of which determines the liring voltage of the tube witha` given spacing between the ano-de and cathode, said inert gas having a relatively low coefficient of expansion so that the gas pressure remains substantially constant during varying temperature conditions, and said gas being resistant to absorption by the mercury and having good spark quenching characteristics.

2. A high voltage discharge device suitable for controlling the discharge of a condenser in a condenser discharge type electric fence controller wherein the condenser spontaneously discharges through the device to place an eiective shock on the fence comprising: a discharge tube having an envelope from which air has been evacuated; means for mounting the envelope in an upright position; means for ring and controlling discharge of the tube including a pair of spaced apart electrodes and an inert gas inside said envelope, one of said electrodes being a pool of mercury in the bottom of the envelope and providing a cold cathode for the tube, the other electrode being of solid metal and being rigidly mounted in the envelope and having its portion adjacent to the surface of the pool of mercury of such size and shape that the spacing between it and the mercury remains substantially constant throughout a relatively wide range of possible inclination of the envelope from its intended upright position, and said inert gas being spectroscopically pure helium, the pressure of the helium and the spacing of the electrodes being such as to permit firing and discharge of the tube only upon impression of a predetermined high voltage across the electrodes of the tube and to at all other times prevent arcing between said electrodes.

3. A gaseous discharge tube suitable for controlling the discharge of a condenser in a condenser discharge type electric fence controller wherein the tube must be capable of successfully withstanding relatively heavy loads without change in its factors determining the firing voltage of the tube comprising: an envelope from which air has been evacuated; means for mounting the envelope in an upright position; an insert in the bottom of the envelope formed of refractory material and having a concave top surface leading from the side Walls of the envelope and converging down to the mouth of an open central well in the insert; a conductor leading from the bottom of the Well through the wall of the glass envelope to the exterior thereof; a quantity of 'mercury in said well providing a cold cathode for the tube, said Well holding the mercury spaced from the glass Walls of the envelope to thereby preclude the arcs which occur during firing of the tube from striking the glass; and an anode supported from the upper portion of the tube and extending down toward the mercury but spaced therefrom.

STANLEY G. KLUMB. 

